The present invention relates to a hand circular saw with a swinging protective hood and a miter angle adjusting device.
One of such hand circular saws is disclosed in U.S. Pat. No. 4,856,394. The hand circular saw disclosed in this reference has a swinging protective hood, a cutting depth adjusting device and a miter angle adjusting device. The cutting depth is determined by the distance of the projection of the saw blade under the base plate. For its adjustment the saw blade is turned up and down relative to the base plate about an axis extending parallel to the rotary axis of the saw blade and is arrested in a desired position by clamping means relative to the base plate. The base plate protects the hand circular saw on a workpiece, so that an angular adjustment of the saw blade relative to the workpiece is obtained not in a freely hanging manner, but instead in a supported manner. In this construction the adjusting devices impart to the saw blade a high freedom degree with accurate guidance relative to the workpiece.
Hand circular saws with swinging protective hoods are used predominantly for displacement sawing and only as an exception for plunge sawing. During the displacement sawing the cutting depth is preselected, and the housing is arrested relative to the cutting depth guiding bucket with the preselected value. The cutting depth adjusting device is loaded in their bearings and guides only a little, namely only by the weight force of the saw.
In contrast, during the plunge sawing, in addition to the weight forces also the reaction forces act on the cutting depth adjusting device due to the tool engagement with the workpiece. There is therefore the danger that the saw blade during the upward and downward swinging is displaced or tilted unintentionally from its plane perpendicular to the base plate. Therefore deviations from the nominal position can lead to canting of the saw blade in the saw gap and as a result undesirable high quantity of chips is removed.
The miter angle adjusting device during "standard horizontal cut" and during plunge sawing are subject to the same conditions as the cutting depth adjusting device. For adjusting the miter angle the saw is turned about a turning axis parallel to the saw blade and to the base plate. The bearing or coulisse which forms the turning axis are arranged at a relative great distance from one another of at least approximately 200 mm. Moreover, the gripping point of the hand of the operator during the inclined adjustment of the hand circular saw is located far from the bearing or the bearings. Therefore a long arm is produced, and as a result the adjusting forces during the incline adjustment produce high rotary or bending moments on the hand circular saw. They can lead to twisting or canting of the parts which carry the bearing, so that the hand circular saw is turned in a bearing by 45.degree. and in the opposite bearing by 43.degree.. Because of this difference for adjustment of the miter angle, disturbing inclined positions of the saw blade relative to the base plate or to the predetermined cutting plane occur. Such inclined positions lead to inclined cutting edges and thereby to faulty saw cutting. This danger is characteristic especially for hand circular saws with coulisse guides for miter angle adjustment, which have the advantage of dispensing with a physical turning axis formed by the bearing block or rotary pin, wherein for the same tool engaging line at all miter angles the turning axis extends under the base plate or on the workpiece.
The known coulisses which form the bearing are composed of a metal sheet with a punched guiding slot which forms a guiding track for a coulisse block. The width of the guiding track is determined by the thickness of the metal sheet. Thereby a high surface pressure is produced in the guiding slot, and as a result, a high friction occurs which leads to difficulties and/or high wear.
The known hand circular saws have relatively exactly guiding coulisse with a guiding track which is formed by a guiding slot of a predetermined width and guides the coulisse block in a substantially gap-free manner. These coulisses however have exclusively guiding functions and the coulisse block is not clampable in them.
For the production of the guiding slots and coulisse blocks very narrow tolerances must be provided. Therefore, the machining expense is high. Moreover, the guiding slot and the coulisse block are wear sensitive. The higher the wear, the greater is the guiding gap between the coulisse block and the guide, and the greater the deviation of the position of the turning axis from its ideal position.
For arresting the turning axle, in addition to the coulisse, clamping means in form of additional clamping coulisse is arranged between the housing and the base plate. Threaded bolts which extend into the gap and are clampable by clamping screws are fixedly connected with the housing and guided in the clamping slow with coarse tolerances. They must follow the movement provided by the guiding coulisse so as to clamp each desired miter angle position.
The threaded bolts described hereinabove are arranged in general parallel to the turning axis. Thereby the clamping screw is accessible for the operator only from the side. Moreover, it is conventional to read the scale which is mounted on the clamping coulisse for indicating the miter angle only from the front or from the rear, and not from above, from the view of the operator. This makes difficult the controlled adjustment and preselection of a miter angle.